1. Field of the Invention
The present invention relates to an electronic control and, in particular, to an improved control for a copy system wherein documents are scheduled (i.e., components of the copy system are instructed when to perform specified functions relating to that document) at a time which is separate from the time at which a copy sheet which is to receive the image contained on the document is scheduled (i.e., components of the copy system are instructed when to perform specified functions relating to that copy sheet).
2. Discussion of Related Art
Copy machines typically provide a photoconductive belt or drum (hereafter referred to only as a belt) which is rotated and receives a latent image of one or more original documents thereon. The latent image can be formed on the photoconductive belt by directing a stream of light which is modulated according to the image contained on an original document towards the photoconductive belt. This stream of light can be formed, for example, by reflecting a beam of light off of the original document and onto the photoconductive belt, or by scanning the document with an electronic scanner to produce a data signal and converting the data signal to a light signal (e.g., an imagewise modulated laser beam) which is then directed to the photoconductive belt. Alternatively, a stream of ions can be directed towards an electroreceptive surface (contained, for example, on a belt or drum) so as, to imagewise charge the electroreceptive surface and form a latent image thereon. These various fashions of forming a latent image on a surface, such as a photoreceptive or electroreceptive surface, from an original document are generally referred to as "imaging" that document.
In a copy machine, the photo or electroconductive belt or drum (hereinafter referred to merely as a photoconductive belt) is often divided into "pitches". Each pitch represents one image at various stages of the reproduction process. Usually, there are more than one image or pitch on the belt at any one time. In the control of the copy machine, therefore, to time various events related to various pitches, it is necessary to track according to each pitch the time that a particular event should occur in relation to that particular pitch. This is done by timed clock signals related to each pitch in order to synchronize the events of the machine and coordinate the various events. See, for example, U.S. Pat. No. 4,588,284 to Federico et al.
The terminology "scheduling" refers generally to the process of instructing one or more components (or subsystems) of the copy machine when to perform one or more specified functions related to an original document to be copied (hereafter referred to as a document) and/or to a sheet which is to receive the image contained on that document (hereafter referred to as a copy sheet). Thus, "scheduling" involves instructing a component of a copy system at what time, relative to a reference time, that component is to perform its specified function. Typically, some point along the circumference of the belt acts as a reference point (usually falling between consecutive pitches) from which all events are to occur. For example, the time at which this reference point is located at a certain position in the copy machine is designated as a reference time, and the time at which various events are to occur are designated relative to this reference time. Since the belt is moved at a substantially constant velocity, the location of any particular portion (or pitch) of the belt can be continuously tracked by a main controller (or Job Manager) which oversees the functioning of all the components of the copy machine.
The Job Manager instructs each of the components of the copy machine when to perform its respective function relative to each document to be imaged, and relative to each copy sheet which is to receive an image from a respective document so that the images contained on consecutive documents are output onto consecutive copy sheets. In other words, the Job Manager instructs the imaging system when to image a document placed on a platen of the copy machine so as to produce an image signal representative of the image contained on that document and to project that signal onto a pitch of the photoconductive belt. The Job Manager also instructs a copy sheet feed system when to feed a copy sheet towards a transfer station where the developed image formed on the photoconductive belt is transferred to the copy sheet so that the copy sheet will arrive at the transfer station at substantially the same time that the pitch containing the image from that document arrives at the transfer station. This scheduling process is performed for each document to be copied. Additionally, when the copy machine includes a recirculating document handler (RDH) or a universal document handler (UDH) that includes an RDH, the Job Manager also instructs the RDH when to feed a document from a set of documents, usually contained as a stack in a tray of the RDH, from the stack onto the platen for being imaged.
It is desirable to continuously feed documents from the stack of documents onto the platen so that each consecutive document is imaged onto a consecutive pitch of the photoconductive belt without skipping any pitches. When a pitch is skipped, a portion of the photoconductive belt which is large enough to receive a latent image of an original document is left blank (is not imaged) and thus is not fully utilized. These blank portions are also known as "skipped pitches". Skipped pitches decrease the speed at which a set of documents can be copied and also reduce the overall efficiency of the copy machine because the components of the copy machine experience wear-and-tear even if an image is not formed on a pitch (i.e., the belt continues to rotate even if no image is formed on a pitch). Thus, it is not desirable to skip pitches on the photoconductive belt.
It is also common for a document handler and copy machine to be used to copy documents having a variety of sizes (i.e., length-by-width sizes). Since the size of documents can vary, the amount of space required on the photoconductive belt to hold the latent image of a document (the size of the pitch) also varies. Thus, it is not uncommon for a copy machine to be operable in a number of modes of operation, each mode being for a different sized sheet, wherein the photoconductive belt has a different number of pitches depending on the size sheet to be imaged in that mode. For example, a copy machine may be operable in: a six pitch timing mode when it is imaging B5, A4, or 81/2 inch wide documents; a five pitch timing mode when imaging B4 size documents; or a four pitch timing mode for imaging A3 and 11.times.17 inch documents. Obviously, the larger the size of the document to be imaged, the fewer number of pitches which are contained on the photoconductive belt.
In previous systems, the Job Manager or device which performed the scheduling of the various events to take place in the copy machine instructed each component of the copy machine when it was to perform its particular function for a particular document at the same time (usually shortly after the pitch which is to receive the latent image of a document passes a reference point). For example, the scheduling device would instruct: (a) the RDH when to begin feeding a document to the platen; (b) the imaging system when to begin imaging the document; and (c) the copy sheet feed system when to begin feeding a copy sheet towards the transfer station to receive the developed latent image of the document contained on the photoconductive belt, at the same time.
However, a problem arises in some copy machines due to the configuration of the RDH used therewith. This problem involves the detection of the last document in the set of documents. RDH's typically use an arm as an end-of-set detector, which is placed on top of the stack of documents prior to starting the imaging thereof, to determine when the last document in the stack of documents has been removed from the RDH. When the last document (which was the top document of the stack prior to starting the imaging) is removed from the RDH, the arm touches an electrical contact to provide a signal indicating the end of the set of documents. The location of the end of the set, and in particular, the knowledge that the last document in the set of documents is being fed through the copy machine is important for a number of reasons. For example, when a job involves making multiple copies of a set of documents, the end-of-set signal indicates the completion of each consecutive copy of that set of documents. This knowledge can be used to offset each copy of the set of documents. Additionally, the knowledge that the last document in the stack of documents is being fed through the copy machine is necessary when the last document in the stack of documents must be reproduced onto a special type of copy sheet. Usually the stack of documents is placed face-up in the RDH and the documents are fed from the bottom of the stack in N-1 order wherein the top document in the stack (and thus the last document to be fed through the RDH) is the cover sheet of the set of documents. It is frequently desired to have the cover sheet of a set of documents printed on a special type of paper (e.g., having a different stiffness, color, or other quality from the other copy sheets in the stack of documents). However, some RDH's have an end-of-set detector which is placed in a position, relative to the stack of documents and the direction which documents are removed from the stack, which does not always permit the removal of the last document from the stack of documents to be detected until after that last document has been scheduled by the Job Manager. In this situation, it was not possible for the image on that last document to be easily reproduced on a special type of copy sheet.
In some RDH's, such as RDH 100 illustrated in FIG. 1A, the removal of the last document of a stack of documents from the tray 104 which holds the stack is detected shortly after the last document begins to move from tray 104 regardless of the size of that document. RDH 100 includes a movable back wall 108 which moves in the directions indicated by arrow A and is set depending on the size of the documents being imaged, and a movable side wall 112 which moves in the direction of arrow B and is set depending on the length of the documents being imaged. Additionally, an end-of-set detector arm 116 is provided and attached within movable back wall 108 so as to be movable with back wall 108. Arm 116 is automatically placed on the top of the stack of documents prior to starting imaging of the stack of documents and touches contact 120 (located below tray 104) to provide an end-of-set signal shortly after the last document in the stack of documents is removed therefrom. The documents are removed from the stack in the direction of arrow C and placed on a platen located below RDH 100. As can be seen in FIG. 1A, the arm 116 will always touch contact 120 shortly after the last document begins moving from tray 104 because arm contacts the trailing edge of the documents as they are removed from tray 104.
However, RDH's having the arrangement illustrated in FIG. 1B operate somewhat differently. RDH 200 includes a tray 204, movable back wall 208 and movable side wall 212, similar to those shown in FIG. 1A. The end-of-set arm 216 and contact 220, however, are located at a fixed position near a side of tray 204 relative to the feed direction C. Since RDH 200 must be used with a variety of widely different sized documents, arms 216 and contact 220 must be located closely adjacent to a forward edge of tray 204 (relative to feed direction C) so that it can be used with sheets having a small width. Consequently, when RDH 200 is used with larger sized documents, arm 216 does not touch contact 220 until the last larger sized document is fed almost entirely out of tray 214. Depending on the type of copy machine used with RDH 200, the scheduling for the last document in the stack of documents will have been performed before the trailing edge of that last document passes arm 216, and thus the end-of-set signal will not be provided in time to place the correct type of copy sheet in the path which leads to the transfer station. In some machines, the scheduling of the imaging of a document must be performed very early during the process of removing the document from the tray 204 (i.e., prior to the time when the trailing edge of the document passes arm 216) so that the imaging system is ready to image that document as soon as it is placed on the platen, and so the next document can be fed to the platen immediately without skipping pitches. Since the scheduling of the copy sheet feed system is performed in previous copy machines at the same time as the scheduling of the imaging system, the copy sheet feed system was scheduled before the Job Manager could be provided with an end-of-set signal.
The above described problem has been addressed in the prior art as follows. Skipped pitches were placed between each document in the scheduling scheme so that adequate time was provided for detecting whether a document is the last document in the stack of documents. In this "skipped pitch" mode of operation, instead of scheduling the imaging system and the copy sheet feed system very early in the process of document removal from tray 204, the Job Manager waited one entire pitch until scheduling the imaging system and copy sheet feed system. By waiting one entire pitch, time was provided for the trailing edge of very large documents (e.g., 11.times.17" documents) to pass arm 216 so the Job Manager could receive the end-of-set signal. However, a pitch on the photoconductive belt (which continuously moves) had to be skipped between each document in the set in order for sufficient time to pass for the trailing edge of the last document to move past arm 216. Alternatively, the entire stack of documents was fed through the RDH without imaging thereof so that the number of documents in the set could be counted (this is known as precounting). Once the number of sheets in the stack was know, the Job Manager would automatically designate the correct type of copy sheet for receiving the image from the last document in the set of documents. The disadvantages of providing skipped pitches have been discussed above. Precounting has the disadvantages in that the total time required to image a stack of documents is increased. Depending on the size of the stack (or set) of documents, the precounting time can be sizable. The number of times which documents must be cycled through the RDH also increases the possibility of paper jams occurring.
U.S. Pat. No. 3,917,396 to Donohue et al. discloses a control system for controlling the processing steps of an electrostatic printing machine. The system includes a means for generating a series train of clock pulses, a means for generating a series train of start or reset pulses and control logic to generate a plurality of timed control signals used to implement processing steps.
U.S. Pat. No. 4,588,284 to Federico et al. discloses a control system which automatically alters control of a machine to respond to a different number of pitches or images. A pitch reset signal is generated by a paper handling remote control board. The reset signal is generated in response to a sensed registration finger. Specific processing steps such as development, cleaning, exposure, etc. are timed and controlled by the pitch reset signal and clock signals.
U.S. Pat. No. 4,800,482 to Hosaka et al. discloses a sequence controller for a copy machine which performs sequence timing control of electronic equipment in a predetermined order.
U.S. Pat. No. 4,816,868 to Shimizu et al. discloses an image forming apparatus in which copying operations are controlled according to a program sequence.
U.S. Pat. No. 4,589,645 to Tracy discloses a document set separator and stack height sensor which is used to provide an end-of-set signal.
Some examples of Xerox Corporation RDH U.S. Patents are U.S. Pat. No. 4,459,013 issued Jul. 10, 1984 to T. J. Hamlin et al.; U.S. Pat. No. 4,278,344 issued Jul. 14, 1981 to R. B. Sahay; and U.S. Pat. Nos. 4,579,444, 4,579,325 or 4,579,326. Some other examples of recirculating document handlers are disclosed in U.S. Pat. Nos. 4,076,408; 4,176,945; 4,428,667; 4,330,197; 4,466,733 and 4,544,148. A preferred vacuum corrugating feeder air knife, and a tray, for an RDH, are disclosed in U.S. Pat. Nos. 4,418,905 and 4,462,586. An integral semiautomatic and computer form feeder (SADH/CFF), which may be an integral part of an RDH, as noted in Col. 2, paragraph 2, therein, is disclosed in U.S. Pat. No. 4,462,527. Various other of these patents, such as U.S. Pat. No. 4,176,945 above, issued Dec. 4, 1979 to R. Holzhauser (Kodak) teach plural mode, e.g. RDH/SADH, document handlers.
As to control systems, some examples of various other prior art copiers with document handlers with control systems therefor, including document sheet detecting switches, sensors, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270; and 4,475,156. In an RDH, a document set separator conventionally counts document set recirculations by signaling each time the last document of the set is fed. See, e.g., U.S. Pat. No. 4,589,645. It is well known in general and preferable to program and execute document handler and copier control functions and logic with conventional software instructions for conventional microprocessors. This is taught by the above and other patents and various commercial copiers. Such software may of course vary depending on the particular function and the particular software system and the particular microprocessor or microcomputer system being utilized, but will be available to or readily programmable by those skilled in the applicable arts without undue experimentation from either the provided verbal functional descriptions, such as those provided herein, or prior knowledge of those functions which are conventional, together with general knowledge in the software and computer arts. Controls may alternatively be provided utilizing various other known or suitable hardwired logic or switching systems.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background.